Field of the Invention
The present invention relates to a balancer apparatus for an internal combustion engine wherein, between a crankshaft supported for rotation on a crankcase which configures part of an engine main body and a balancer shaft having a balance weight and supported for rotation on the crankcase so as to have an axial line parallel to the crankshaft, a gear transmission mechanism is provided that includes a driven gear wheel fixed to the balancer shaft.
Description of Background Art
A balancer apparatus for an internal combustion engine is known. See, for example, Japanese Utility Model Laid-Open No. Hei 7-18051 and Japanese Patent Laid-Open No. 2010-236499.
In the balancer apparatus for an internal combustion engine disclosed in Japanese Utility Model Laid-Open No. Hei 7-18051 and Japanese Patent Laid-Open No. 2010-236499 mentioned above, in order to fulfill the positioning of a driven gear wheel around an axial line with respect to a crankshaft, a woodruff key is fitted in a keyway provided on an outer periphery of a balancer shaft at a portion wherein the balancer shaft is fitted and a keyway provided on an inner periphery of an attachment hole is provided in the driven gear wheel for fitting the balancer shaft therein. This gives rise to the necessity to upsize the balancer shaft as the transmission torque between the driven gear wheel and the balancer shaft increases.